A valve seat is a part that serves as a seat of an air valve or an exhaust valve, the part being connected to the valve and needed for maintaining air-tightness of a combustion chamber.
A valve seat has the following requirements: (1) a function of maintaining air-tightness in order to prevent leakage of compressed gas or combustion gas into a manifold; (2) a heat-conducting function for allowing heat in the valve to escape toward the cylinder head; (3) sufficient strength to withstand impact on the valve during seating; and (4) a wear-resistance function minimizing wear even in high-heat and high-load environments.
Additional required characteristics of a valve seat include: (5) lacking aggressiveness to the associated valve; (6) having a reasonable cost; and (7) being easy to scrape during processing.
An iron-based sintered alloy therefore is used in a valve seat so as to satisfy the functions and characteristics stated above.
For example, patent document 1 discloses a valve seat made of an iron-based sintered alloy, in which voids are filled with an organic compound and at least the outer perimeter surface is sealed with triiron tetroxide.
Patent 2 discloses a valve seat containing an iron-based sintered alloy, in which the iron-based sintered alloy is used as a base material and the surface is covered with an iron oxide film mainly composed of triiron tetroxide.